ROBERTd'Oilgi, d'Oilly, or d'Oyly (d. 1090?), Norman baron, was probably a native of Ouilly-le-Vicomte, near Lisieux, and, with his brothers Nigel and Gilbert, came to England with William the Conqueror. Robert was very soon rewarded with large grants of land in the Midland counties, and with the hand of Alditha (Ealdgyth), the heiress of the wealthy thane Wiggod of Wallingford, kinsman and cupbearer of King Edward. In 1071 Robert was ordered by the king to build a castle at Oxford, and is therefore known as ‘constabularius Oxoniæ,’ or ‘castelli urbis Oxenefordensis oppidanus’ (Hist. Abend. ii. 7, 12). The great tower of the keep, which still remains, though in the native or primitive Romanesque style, is almost certainly his work. In 1074 he founded the church of St. George in Oxford Castle for secular priests, with a small endowment (the rectory of St. Mary Magdalen), afterwards increased; this foundation was annexed to Oseney Abbey about 1149; but the crypt of the church is still preserved under Oxford gaol, though the stones have been moved from the original site. In later life, Robert, who is described as very rich and grasping, was induced by a dream to restore to Abbot Rainald lands which he had seized belonging to the abbey of Abingdon. He also became generally a ‘reparator ecclesiarum et recreator pauperum,’ and is supposed to have built the existing tower of St. Michael's, at the North Gate of Oxford (which is in the same style as the castle keep), the original church of St. Mary Magdalen, and the remarkable crypt of St. Peter's-in-the-East, the endowment of which was supplied from his manor of Holywell (Domesday, p. 158 b). He also built a bridge in the north-west of Oxford, now Hythe bridge (Hist. Abend. ii. 15). At Easter 1084 he entertained Prince Henry, with St. Osmund and Miles Crispin, at Abingdon Abbey, providing both for them and for the monks. There is no good evidence that the castle and priory of Wallingford were erected by him.

Robert d'Oilgi died in September, probably in 1090; he and his wife were buried on the north side of the high altar at Abingdon. The great fee of Oilly, which included about twenty-eight manors in Oxfordshire, passed to his brother Nigel, whose name occurs frequently in Oxfordshire and Berkshire charters till about 1119. By his wife Agnes Nigel had two sons, Robert and Fulk, the former of whom, Robert d'Oilgi II (fl. 1130–1142), was ‘constabularius regis Henrici primi,’ and became ‘civitatis Oxnefordiæ sub rege præceptor’ (Gesta. Stephani, p. 74; Ann. Mon. iv. 19). In the war between Stephen and Matilda, Robert, who is called in the ‘Gesta Stephani’ ‘vir mollis et deliciis magis quam animi fortitudine affluens,’ took the side of the empress. He went to her at Reading in 1141, and invited her to Oxford Castle, where she was besieged by Stephen (October–December 1142), and eventually obliged to escape on the ice to Wallingford. The Oseney chronicler states definitely, although the statement is difficult to reconcile with mention of him in an assumably later charter at Oseney (Mon. Angl. vi. 251, No. iv.), that Robert d'Oilgi II died fifteen days before this siege, and was buried at Eynsham (Ann. Mon. iv. 24). Kennet (Par. Ant. i. 155–8) infers from certain payments to the sheriffs of Oxfordshire in 1155 and 1157 that Robert died about 1156.

Robert received in marriage the king's mistress, Edith, daughter of Forne, lord of Greystock, with Steeple Claydon in Buckinghamshire as her dower. He left two sons, Henry d'Oilgi I (d. 1163), and Gilbert. The barony, on the death of Henry d'Oilgi II, passed to the family of his sister Margaret, the wife of Henry Newburgh, earl of Warwick. Robert and his wife Edith, with Robert, her son by King Henry, are remarkable for their munificence to religious bodies, such as the Templars of Cowley near Oxford (1143), the Cistercians of Oddington or Thame (c. 1138), and the abbeys of Eynsham, Gloucester, and Godstow. Their most important work was the foundation of Oseney Abbey for Austin canons on a branch of the Thames near Oxford, at a spot where Edith had noticed the noise of ‘chattering pyes,’ explained by her confessor, Ranulph, a canon of St. Frideswide's, as the complaints of souls in purgatory. The original endowment, in 1129, included the tithes of six manors and other estates, and was largely augmented in 1149 by the annexation of St. George in the Castle, with its increased property, and by many other lands in the fee of Oilly. St. George's was afterwards used by the abbey for the accommodation of their students at the university, and Henry V at one time intended to turn it into a large college. Wiggod, the second prior and first abbot of Oseney (1138–1168), was probably related to the wife of Robert d'Oilgi I.

Kennet and others attribute to Edith d'Oilgi the foundation of Godstow priory, about 1138; but the only evidence for this is that the foundress (who seems to have been a widow) bore the same Christian name. Leland saw at Oseney the tomb of Edith, with her effigy ‘in thabbite of a vowess,’ and a mural painting of the pyes and Ranulph.

[The original authorities are the Chronicles of Abingdon and Oseney (Rolls Ser.), and the Gesta Stephani and Continuator of Flor. Wig. (Engl. Hist. Soc.), thecharters, &c., in Dugdale's Mon. Angl. vi. 1461–3 (St. George's), and 248–252 (Oseney), and v. 403 (Thame), the Domesday Survey, passim, but esp. Oxfordshire, pp. 154 a, 158 a, 158 b. The results are well put together in Freeman's Norman Conquest, iv. 44–7 and 728–34, and still better in Mr. James Parker's Early History of Oxford, with special reference to the buildings. The notices in Wood's City of Oxford (ed. Clark, i. 265–78), Kennett's Parochial Antiquities, i. 75–158, Dunkin's Bicester, &c., W. D. Bayley's House of D'Oyley, and J. K. Hedges's History of Wallingford, vol. i., do not distinguish with sufficient accuracy between facts, inferences, and conjectures.]